(1) Field of the Invention
The present invention relates to enhancements in security devices and, particularly, to the generation of signals commensurate with the state of a mechanical closure member through which access to a secured device or area is obtained. More specifically, this invention is directed to an improved safety switch unit and, especially, to a signal generator for monitoring the position of a protective cover and providing command and/or control signals commensurate with whether that cover is in an open or closed condition. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
Devices for monitoring the position of protective covers, and producing command signals which energize a warning device and/or activate a disabling device, are well-known in the art. By way of example, German Patent 1,553,550 discloses a stop device for a damper which opens via a heat-sensitive cut-out. In this prior art device, a holder for a stop bolt is affixed to the inside of the damper, the stop bolt being movably mounted in the holder and being normally blocked by a stop member. When the cut-out is released, the stop member enables the stop bolt to move either under the influence of gravity or in response to a spring bias. However, in this rather primitive early device, there is no provision for monitoring the open and closed positions of the damper.
Another example of the prior art is disclosed in published German Patent Application 40 13 994. This published application is directed to a safety switch, which is associated with a door or the like, the door rotating about a shaft. The safety switch is provided with a disk-shaped actuating cam. This actuating cam also rotates about the shaft, in response to movement of the door, and simultaneously actuates, via tappets, a pair of switches. In the safety switch of the published application, the actuating cam is seated on the shaft about which the door rotates and, accordingly, both assembly of the device and subsequent adjustment for proper operation are difficult. Indeed, such difficulties seriously limit the ability to retrofit existing protective covers with such a prior art safety switch device.